Enzymes are the most important chemical mediators of every living cell's activities. These organic substances catalyze, or promote, the uptake and use of raw materials needed for synthesis of cellular components or for energy. Enzymes are also involved in the breakdown of unneeded substances or of metabolic side products that must be eliminated from the cell and returned to the environment.
As catalysts, enzymes promote changes only in very specific substances or substrates, as they are often called. Thus, in the previous exercise, the changes produced in simple carbohydrates and in starch substrates were brought about by different, specific enzymes. We have seen the activity of an enzyme with a different kind of outcome, the breakdown of an antimicrobial agent (see Experiment 15.3), but the principle is exactly the same. In the latter instance, the beta-lactamase enzyme penicillinase brought about a change in the substrate penicillin.
Since enzymes appear to be limited to particular substrates, it follows that each bacterial cell must possess a large battery of different enzymes, each mediating a different metabolic process. They are identified in terms of the type of change produced in the substrate. In naming them, the suffix -ase is usually added to the name of the substrate affected. Thus, urease is an enzyme that degrades urea, gelatinase breaks down gelatin (a protein), penicillinase inactivates penicillin, and so on.
In this exercise, we shall see how many bacterial enzymes are demonstrated and how their recognition in bacterial cultures leads to identification of species.
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